Some wind turbines utilize a rotor which includes one or more fixed pitch, airfoil blades. The blades are connected via a teetering hub, a shaft and a gearbox to an electric generator or alternator The power output of the wind turbine is regulated by controlling the angle (known as yaw angle) between a plane formed by the rotating blades and the direction of the wind. Full power may be achieved when the plane of the blades is perpendicular to the direction of the wind (i.e. "into" the wind). No power is achieved (and the aerodynamic torque upon the rotor is minimized) when the plane of the blades is parallel to the direction of the wind (i.e. "out" of the wind). The power output of the system may be varied by yawing the rotor angularly by degree into and out of the wind.
Some systems have automatic controls which set the yaw angle to optimize the power output of the system. In an emergency, as when the system load is lost or the automatic control has lost power, the wind turbine must be yawed out of the wind to prevent the blades from overspeeding. Overspeeding may cause severe damage to wind turbine components.